This invention relates to apparatus and methods for moulding straps on groups of battery plates.
In GB-A-2023471 a moulding system is described in which a mould consists of a number of mould cavities for forming battery straps, which are fed from a single feed channel over respective weirs. The process involves pumping lead into the feed channel from a lead pot so that the lead overflows the weirs and dipping the lugs of the groups of battery plates into respective cavities whilst the lead is still hot. Once the lead has been pumped for a sufficient time to fill the cavities, the pumping is stopped and excess lead flows back into the feed line either under positive pumping or, more usually, as a result of a return valve opening to allow gravitational feed of lead back into the lead pot. If a mould having this so called “tidal flow” characteristic is operated without any battery plates being dipped, the cavities fill very precisely to the level defined by the weirs. However, in practice, the cooling of the lead in the cavity created by the introduction of the solid lugs actually tends to mean that the moulded strap thickness are determined by the amount of lead which is poured into the cavity.
Originally the “tidal flow” system worked well, because machines were operated at a cycle time which allowed the lead in the feed pipe to settle back to a constant datum level. However, automation of many parts of the manufacturing line for batteries, has meant that cycle times have had to be decreased throughout the process and it is frequently the case that during the main running part of the operation of such moulding apparatus the lead in the feed pipe does not fall all the way back to the datum, because the final part of any drain cycle is rather slow. However, when the machine is stopped for maintenance or changing a mould, full drain back does take place. The result is that straps of different thickness are produced depending when, in the production cycle, they are formed.